Device and method for discharging sealing air in a turbofan engine

ABSTRACT

A device and method for discharging sealing air in a turbofan engine includes a primary flow duct that extends through a core engine of the turbofan engine and a bypass duct. The device has at least one bearing chamber sealed by sealing air of the turbofan engine, said bearing chamber surrounding at least one oil-lubricated bearing element for mounting a mechanical component of the turbofan engine. At least one discharge path for escaping sealing air is provided, which extends up to the bypass duct of the turbofan engine.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application No.DE102013213520.3 filed on Jul. 10, 2013, the entirety of which isincorporated by reference herein.

BACKGROUND

This invention relates to a device and a method for discharging sealingair in a turbofan engine.

An aircraft engine at least includes a compressor, a combustion chamberand at least one turbine. A compressor and a turbine are connected hereto one another via a shaft. Such a shaft is mounted in a bearing chamberwith bearing elements that are lubricated and cooled with oil. The oilis usually drawn from an oil tank, supplied by means of an oil conveyingpump to the bearing chamber and to the bearing elements, and returned tothe oil tank via an oil suction pump.

To prevent any leakage of oil out of the bearing chambers, the latterare provided with seals and additionally subjected to sealing air fromthe outside. This sealing air forms an excess pressure (sealingpressure) around the bearing chambers and the seals, so that a positivepressure ratio is achieved at the bearing chamber seals. This means thatthe air pressure outside the bearing chamber, i.e. the sealing pressure,is greater than the air pressure inside the bearing chamber (so-calledchamber pressure). With this positive pressure ratio, air flows into thebearing chamber via the seals and thus prevents oil leaking from thelatter. The sealing air is drawn from the compressor of theturbomachine, usually as compressor bleed air, and supplied to thebearing chamber from the outside. It cannot be avoided here that excesssealing air escapes via a seal to a certain extent, and is guided intothe airflow to the core engine.

Known sealing air systems are disadvantageous in that under certainconditions, in particular during transition between different operatingstates of the engine, the sealing air supply to the seals of the bearingchamber can be too low, such that the sealing pressure is insufficientto obtain a positive pressure ratio at the bearing chamber seals. Thiscan result in oil leaking from the bearing chamber. An oil leakage mayalso be caused by wear on the bearing chamber seals. Such an oil leakagehas the effect that oil is guided into the airflow to the core engineand from there into the bleed line for supplying fresh air to theaircraft, resulting in a contamination of the cabin air that is harmfulto health.

SUMMARY

An object underlying the present invention is to provide a device and amethod for discharging sealing air in a turbofan engine that preventsthe contamination of cabin air even in the event of lubricating oilexiting the bearing chambers.

The solution in accordance with the invention provides a device fordischarging sealing air in a turbofan engine, said device forming adischarge path for escaping sealing air which extends up to the bypassduct of the turbofan engine. The discharge path thus extends from apoint at which possibly oil-contaminated sealing air escapes, up to thebypass duct of the turbofan engine. This point can for example be asealing air seal from which sealing air is escaping.

In the event that lubricating oil exits the bearing chamber via bearingchamber seals and mixes with the sealing air, it is ensured in this waythat the sealing air contaminated with lubricating oil is not passedinto the primary flow duct and through the core engine of the turbofanengine, but instead into the bypass duct of the turbofan engine.

The solution in accordance with the invention thus prevents, bydischarging contaminated sealing air into the bypass duct of theturbofan engine, said contaminated sealing air from entering acompressor of the core engine and being tapped from there for fresh airsupply and pressure control of the aircraft cabin.

According to an embodiment of the invention, the discharge path forescaping excess sealing air extends through at least one stator wheel ofthe primary flow duct. This is for example a stator wheel arranged atthe start of the primary flow duct to remove from the airflow the swirlpreviously imparted to it in an area of the fan close to the hub. Toprovide an air passage for the sealing air, the stator wheel has forexample at least one cavity forming an appropriate air passage.

By providing a section of the discharge path in a stator wheel of theprimary flow duct, the sealing air can, using already existingstructures and without interacting with the air flowing in the primaryflow duct, pass said primary flow duct outwards in the radial direction.Adjoining it, the discharge path is provided up to the bypass duct ofthe turbofan engine.

The discharge path for the sealing air is for example formed by casingand/or wall elements that together form an air passage and therebydefine the discharge path. It can be provided here that the dischargepath extends along cavities already present in a casing.

According to an advantageous embodiment, it is provided that thedischarge path has a seal to a rotating element of the engine, forexample the fan or a rotor of a medium-pressure or high-pressurecompressor, so that contaminated sealing air can escape into the primaryflow duct either not at all or only to an insubstantial degree. Seals ofthis type are for example designed as labyrinth seals or brush seals.

It can for example be provided that the discharge path has at least oneseal to a fan or a rotor of the engine so that a gap is closed between acasing delimiting the discharge path in this area and the fan or rotor,via which gap sealing air might otherwise escape into the primary flowduct.

The device in accordance with the invention is generally speakingsuitable for sealing any bearing chambers of a turbofan engine that haveoil-lubricated bearing elements. According to an embodiment, the bearingchamber is provided with bearing elements for mounting an engine shaft,for example an engine shaft coupling a low-pressure turbine to the fanof the turbofan engine. The bearing elements for mounting the engineshaft form for example an anti-friction bearing, however any otherbearings can also be used.

It is pointed out that in embodiments of the invention, the bearingchamber, which is sealed using sealing air, is arranged in front of thetapping point for the bleed air relative to the axial direction of theengine. The tapping point is located for example at the high-pressurecompressor of the engine. Since the bearing chambers supplied withsealing air are located in front of such a tapping point in the axialdirection, the sealing air can be discharged into an axially front areaof the bypass duct.

The precise section in which the discharge path ends in the bypass ductis generally speaking immaterial. It is only important in accordancewith the invention that sealing air which is possibly contaminated withlubricating oil is guided into the bypass duct of the turbofan engine.It can be provided in design variants that the discharge path in theaxial direction ends in the bypass duct in front of or behind a fanstator wheel arranged in said bypass duct.

In accordance with a further design variant, the device includes anaxially front and an axially rear bearing chamber area. These twobearing chamber areas can be part of a single bearing chamber oralternatively provided by two separate bearing chambers. A dischargepath section starts from each of the bearing chamber areas. The twodischarge path sections combine to form the discharge path that thenends in the bypass duct. In an exemplary embodiment, this combinationtakes place before the exhaust path extends through a stator wheel inthe primary flow duct.

According to an exemplary embodiment, the bearing chamber is suppliedwith sealing air when a sealing air seal associated with the bearingchamber is provided. The sealing air seal, which limits the escape ofsealing air from a supply path, ensures that a defined sealing pressureprevails around the bearing chamber. However, excess sealing air escapesto a certain degree via the sealing air seal, since the latter cannotprevent a certain amount of leakage. The sealing air can here becontaminated with oil that has leaked from the bearing chamber. Thisescaping sealing air or leakage air is discharged via the discharge pathto the bypass duct.

The present invention also relates to a turbofan engine provided with aprimary flow duct, a bypass duct and a device. Here, the discharge pathends in the bypass duct and is designed to guide escaping sealing air,which is possibly contaminated with lubricating oil, into the bypassduct.

According to a further aspect of the invention, the invention relates toa method for discharging sealing air in a turbofan engine, which has thefollowing process steps:

-   -   Supplying of sealing air to a bearing chamber of the turbofan        engine that has at least one oil-lubricated bearing element, and    -   Discharge of escaping sealing air, which can be contaminated        with oil exiting the bearing chamber, to a bypass duct of the        turbofan engine.

In particular, it can be provided that oil-contaminated sealing airexiting a sealing air seal, by which a certain sealing pressure isprovided around the bearing chamber, is discharged into the bypass ductvia the discharge path. The discharge path extends in this case from thesealing air seal up to the bypass duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the following in more detail withreference to the figures of the accompanying drawings, showing severalexemplary embodiments.

FIG. 1 shows components of a first exemplary embodiment of a turbofanengine, illustrating a fan, a primary flow duct, a secondary flow ductand a first design variant of a device for discharging sealing air.

FIG. 2 shows components of a second exemplary embodiment of a turbofanengine, illustrating a fan, a primary flow duct, a secondary flow ductand a second design variant of a device for discharging sealing air.

FIG. 3 shows components of a turbofan engine for providing sealing airto a bearing chamber.

DETAILED DESCRIPTION

For a better understanding of the present invention, a turbofan enginethat provides for supplying a bearing chamber with sealing air but doesnot yet implement the solution in accordance with the invention, isexplained on the basis of FIG. 3.

The section of a turbofan engine shown in FIG. 3 includes a fan stagewith a fan 1, by which the air mass ingested by said fan 1 is passed onthe one hand into a bypass duct 2 and on the other hand into a primaryflow duct 3. The bypass duct 2 and the primary flow duct 3 are hereseparated from one another behind the fan 1 by a splitter 4.

The primary flow duct 3 passes through the core engine that includes—inthe case of a two-shaft engine—a low-pressure compressor, ahigh-pressure compressor, a combustion chamber, a high-pressure turbineand a low-pressure turbine. In the case of a three-shaft engine, amedium-pressure compressor and a medium-pressure turbine areadditionally provided.

In the section shown, a stator wheel 5 and struts 6 are arranged in theprimary flow duct 3. The stator wheel 5 is used to remove from theairflow the swirl imparted to it in the area of the fan 1 close to thehub. The primary flow duct 3 is surrounded by a casing structure 8delimiting the primary flow duct 3 radially on the outside. The primaryflow duct 3 is delimited radially on the inside by appropriate ringsurfaces of the rotors and stators and by adjoining limiting structures.

The bypass duct 2 of the turbofan engine is delimited by an outer casing9 radially on the outside and by the casing structure 8 radially on theinside. A fan stator wheel 71 is here located behind the fan 1 in thebypass duct 2, and performs the function of removing the swirl impartedto the flow by the fan 1 from that flow. Additionally, struts 72 can belocated in the bypass duct 2 behind the fan stator wheel 71 which aredesigned to support structural loads. If the fan stator wheel 71 isitself designed to support structural loads, these struts 72 can bedispensed with.

The engine furthermore includes an engine shaft 11, which in theexemplary embodiment shown is intended to couple a low-pressure turbineof the engine to the fan 1. Bearings, for example anti-frictionbearings, are provided for mounting the engine shaft 1. FIG. 3 shows abearing chamber 12 inside which one or more bearing elements (not shownseparately) are located and which are used for mounting the rotatingengine shaft 11. As already mentioned, the bearing elements form forexample an anti-friction bearing. The bearing elements are lubricatedwith oil and cooled. To do so, lubricating oil is supplied to thebearing chamber in an oil circuit in a manner known per se to the personskilled in the art.

The bearing chamber 12 is sealed using at least one bearing chamber seal14. It is provided here that the bearing chamber seal 14 is additionallysupplied with sealing air 10. Said sealing air 10 is tapped as bleed airfrom a compressor of the engine, for example from the high-pressurecompressor. The bleed air 10 is supplied via a supply path 13 to thebearing chamber 12. The supply path 13 is formed for example by tubesand/or ducts. The sealing air 10 presses on the bearing chamber seal 14,and thereby prevents the exit of oil. The sealing air thus provides asealing pressure on the outside of the bearing chamber 12 which isgreater than the chamber pressure inside the bearing chamber 12.

The bearing chamber seal 14 is for example a labyrinth seal, a carbonseal or a brush seal.

To ensure that a sufficient sealing pressure is applied to the bearingchamber seal 14, a sealing air seal 15 is furthermore provided thatlargely prevents any escape of sealing air 10 from the supply path 13,hence ensuring a sufficient sealing pressure. It can be provided herethat the sealing air seal 15 is provided on the circumference of acavity surrounding the bearing chamber 12 and the bearing chamber seal14 radially on the outside.

It is however the case that sealing air unavoidably escapes through thesealing air seal 15, i.e. leakage air flows through the sealing air seal15. This air is guided as shown by the arrows 16, 17, 18 and past a gapbetween the fan 1 and the adjoining casing into the primary flow duct 3.This leads to problems in the event that lubricating oil exits thebearing chamber 12 and the bearing chamber seal 14 and mixes withsealing air. In this case, the return of oily sealing air into theprimary flow duct 3 leads to the contaminated air being bled into acompressor of the core engine for supplying fresh air to the aircraft,possibly resulting in a contamination of the cabin air that is harmfulto health and is an odour problem.

Reasons for the exit of lubricating oil can be wear on the bearingchamber seal 14 and/or certain operating states of the engine, in whichthe sealing air supply at the seal 14 of the bearing chamber 12 is toolow to ensure a positive pressure ratio at the bearing chamber seal 14.

The inventive solution to remedy the problem described is explained inthe following in light of two exemplary embodiments with reference toFIGS. 1 and 2.

According to the exemplary embodiment of FIG. 1, the turbofan engineincludes a device for discharging sealing air, said device forming adischarge path 20 which extends into the bypass duct 2 of the turbofanengine and is designed to discharge sealing air escaping from thesealing air seal 15, and possibly contaminated with lubricating oil,into the bypass duct 2.

The discharge path 20 extends from the sealing air seal 15 up to thebypass duct 2, so that lubricating oil escaping from the sealing airseal 15 and mixed with sealing air can be supplied via the dischargepath 20 to the bypass duct 2. Additionally, the section between thebearing chamber 12 and/or the bearing chamber seal 14 and the sealingair seal 15 can here be considered as part of the discharge path.

The discharge path 20 includes three sections 21, 22, 23, provided inthe hub-side casing, in the area of the stator wheel 5 and in the areaof the casing structure 8. The first section 21 of the discharge path 20is formed by casing and/or wall elements of a non-rotating hub-sidesupporting structure 30 which extends in the axial direction behind thefan 1. An air passage for formation of the discharge path in thissection 21 is here advantageously provided as far as is possible byalready existing ducts and cavities connected to one another. To preventsealing air from exiting at the transition between the rotating fan 1and the supporting structure 30 and possibly entering the primary flowduct 3, a seal 24 is provided in this area, which can for example be alabyrinth seal. The proportion 25 of sealing air still leaving this seal24 is so small as to be unproblematic.

The second section 22 of the discharge path 20 is provided by means ofthe stator wheel 5 arranged in the primary flow duct 3. In thisconnection, it is for example provided that the stator wheel 5 isdesigned hollow, thereby providing an air passage for the sealing air.In the area of the stator wheel 5, the sealing air possibly contaminatedwith lubricating oil passes the primary flow duct 3 without coming intocontact with the air flowing in the primary flow duct 3.

The third section 23 of the discharge path 20 is provided in the casingstructure 8, which extends in the radial direction between the primaryflow duct 3 and the bypass duct 2 starting from the splitter 4. To doso, appropriate ducts and interconnected cavities are provided in thecasing structure 8 by suitable casing and wall elements.

The discharge path 20 ends in the bypass duct 2, more precisely speakingin the area of the radially inner boundary surface of the bypass duct 2.In the exemplary embodiment shown, the discharge path 20 is designedsuch that it ends in the axial direction behind the fan stator wheel 71in the bypass duct 2. This must however only be understood as anexample. It can also be provided that the discharge path ends in frontof the fan stator wheel 71 or at any other point in the bypass duct.

FIG. 2 shows a further exemplary embodiment of a turbofan engine havinga device for discharging sealing air. In this exemplary embodiment, afurther (second) bearing chamber 32 is present that is located, relativeto the flow direction inside the engine, behind the (first) bearingchamber 12 in the axial direction, as explained with reference toFIG. 1. The second bearing chamber 32 includes at least one bearingelement for mounting a medium-pressure or high-pressure shaft 31coupling a medium-pressure or high-pressure turbine to a medium-pressureor high-pressure compressor 40. The bearing chambers 12, 32 can beseparate bearing chambers or alternatively represent different bearingareas of a single bearing chamber.

Like the bearing chamber 12, the bearing chamber 32 too has a bearingchamber seal 34 which is supplied with sealing air 10. To do so, thesupply path for the sealing air 10 splits into two supply path sections13, 13A which lead on the one hand to the bearing chamber 12 and on theother hand to the bearing chamber 32. The course as shown of the supplypath sections 13, 13A must be understood only as an example here.

The second bearing chamber 32 is furthermore assigned a sealing air seal35 which provides a sufficient sealing pressure around the bearingchamber 32 corresponding to the sealing air seal 15 of the supply pathsection 13.

As explained with reference to FIG. 1 in respect of the sealing air seal15, sealing air which might be contaminated with lubricating oil canleak out via the sealing air seal 35. This sealing air is discharged viaa discharge path section 26. The discharge path section 26 joins thedischarge path section 21, which is designed as shown in FIG. 1 orissues into the latter before the sealing air flows through the statorwheel 5. The discharge path section 26 extends here, adjoining theradially inner boundary of the primary flow duct 3, in the direction ofthe stator wheel 5 and also opposite the flow direction in the primaryflow duct 3.

Further discharge of the sealing air via the sections 22 and 23 of thedischarge path 20 is as explained with reference to FIG. 1.

It is pointed out that the discharge path section 26 too, at thetransition to the rotor 40 of the medium-pressure or high-pressurecompressor 40, forms a seal 27, with the remaining sealing air 28exiting via the seal 27 being negligible. The seal 25 to the rotatingfan 1 and the seal 27 to the rotating rotor 40 thus largely prevent anyexit of sealing air from the discharge paths 21, 26 and ensure that thesealing air, possibly contaminated with lubricating oil, exiting thesealing air seals 15, 35 is passed via the discharge paths 21, 26, 22,23 into the bypass duct 2. Hence the substantial proportion of thesealing air contaminated with lubricating oil is not passed into theairflow for the core engine, but into the bypass duct 2.

The present invention, in its design, is not restricted to the exemplaryembodiments presented above, which are only to be understood asexamples. It is thus possible in alternative embodiments to design thecourse and the structural embodiment of the discharge path 20 forsealing air in a different way. Also, the primary flow duct 3 and thesecondary flow duct 2 can differ in their shape and in respect of theelements arranged inside them from the exemplary embodiments asdescribed. Furthermore, the bearing chamber having oil-lubricatedbearing elements for mounting a mechanical component of the turbofanengine can be a bearing chamber for mounting a different rotating partof the engine, instead of a bearing chamber for an engine shaft.

1. A device for discharging sealing air in a turbofan engine comprisinga primary flow duct that extends through a core engine of the turbofanengine and a bypass duct, where the device has at least one bearingchamber sealed by sealing air of the turbofan engine, said bearingchamber surrounding at least one oil-lubricated bearing element formounting a mechanical component of the turbofan engine, wherein at leastone discharge path for escaping sealing air that extends up to thebypass duct of the turbofan engine.
 2. The device in accordance withclaim 1, wherein the discharge path extends through at least one statorwheel of the primary flow duct.
 3. The device in accordance with claim2, wherein the stator wheel has at least one cavity for providing an airpassage for the sealing air.
 4. The device in accordance with claim 1,wherein the discharge path is formed, at least in some sections, bycasing and/or wall elements that provide an air passage for the sealingair.
 5. The device in accordance with claim 1, wherein the dischargepath has at least one seal to a rotating element of the engine.
 6. Thedevice in accordance with claim 5, wherein the discharge path has atleast one seal to a fan or a rotor of the engine so that a gap issubstantially closed by said seal between a casing delimiting thedischarge path in this area and the fan or rotor.
 7. The device inaccordance with claim 1, wherein the bearing chamber is provided withbearing elements for mounting an engine shaft.
 8. The device inaccordance with claim 1, wherein the bearing chamber is arranged infront of the tapping point for the sealing air relative to the axialdirection of the engine.
 9. The device in accordance with claim 1,wherein the discharge path is designed such that it ends in the bypassduct in front of or behind a fan stator wheel arranged in said bypassduct.
 10. The device in accordance with claim 1, wherein the deviceincludes an axially front bearing chamber area and an axially rearbearing chamber area of one or different bearing chambers, where adischarge path section starts from each of the bearing chamber areas,and the discharge path sections combine to form the discharge path. 11.The device in accordance with claim 10, wherein the discharge pathextends through at least one stator wheel of the primary flow duct andthe combination of the discharge path sections takes place before thedischarge path extends through a stator wheel of the primary flow duct.12. The device in accordance with claim 1, wherein a sealing air seal isassociated with the bearing chamber sealed by sealing air, said sealingair seal providing a defined sealing pressure around the bearingchamber, where excess sealing air—possibly contaminated with oil thathas leaked from the bearing chamber—escapes via the sealing air seal andis discharged via the discharge path to the bypass duct.
 13. A turbofanengine provided with a primary flow duct extending through a core engineof the turbofan engine, a bypass duct and a device having the featuresof claim 1, where the discharge path ends in the bypass duct and isdesigned to guide escaping sealing air into the bypass duct.
 14. Amethod for discharging sealing air in a turbofan engine comprising aprimary flow duct that extends through a core engine of the turbofanengine, and a bypass duct, which method has the following process steps:supplying sealing air to a bearing chamber of the turbofan engine thathas at least one oil-lubricated bearing element, and discharging ofescaping sealing air, which can be contaminated with oil exiting thebearing chamber, to a bypass duct of the turbofan engine.
 15. The methodin accordance with claim 14, wherein oil-contaminated sealing airexiting a sealing air seal is discharged into the bypass duct.